Polyurethane foams, engineering thermoplastics coatings and elastomers are commonly admixed with flame retardants to achieve the desired degree of flame retardancy for the final material desired. Pumpable fluid (or liquid) flame retardant compositions are a preferred class since such pumpable formulations are needed in environments where automation and machine mixing of the various components are used. Examples of the chemical classes for such fluid or liquid flame retardants include brominated aryl flame retardants, such as polybromodiphenyl oxide, and various viscous organophosphorus flame retardants such as the oligomeric phosphate esters, such as the chlorinated oligomeric phosphate esters (e.g. FYROL 99 brand) and the reaction product of 2-chloro-1-propanol phosphate (3:1) with ethylene oxide and phosphorus pentoxide (FYROL PCF brand), and the aromatic oligomeric phosphate esters such as those containing an arylene bridging group derived from a diol such as bisphenol A, hydroquinone or resorcinol.
High viscosity in such fluid or liquid flame retardant compositions can be disadvantageous since it makes the pumping and movement of such compositions more difficult thereby complicating manufacturing operations. It can also hinder the flow of thermoplastic polymers containing such a viscous flame retardant. For example, it is known that polybrominated diphenyl oxide flame retardants are very viscous. U.S. Pat. No. 4,746,682 to J. Green indicates that either alkyl diphenyl phosphates or alkylated triaryl phosphates can be used to achieve blends having acceptably low viscosity as compared to the polybrominated aryl flame retardant itself. Copending U.S. Ser. No. 215,406, filed Mar. 14, 1994, describes the use of triphenyl phosphate as a viscosity reduction additive for viscous flame retardants. However, the relatively low volatility of the triaryl phosphates makes them unsuitable for certain applications where high processing temperatures may cause juicing.